This invention relates to organopolysiloxanes with polyether and ester groups linked to a common spacer group, wherein the spacer group is linked through an SiC bond to the siloxane backbone.
It is well known that polysiloxanes which contain polyether groups that are linked to the polysiloxane backbone by an SiC bond are synthesized by the addition reaction between allyl polyethers and hydrogensiloxanes. Reference is made only to the German Patent 31 33 869 as being representative of the patent literature which deals with this synthesis.
However, it has proven to be disconcerting that, under the conditions of the hydrosilylation, a rearrangement of the allyl polyether to the corresponding propylene polyether takes place in competition with the addition reaction: EQU CH.sub.2 .dbd.CH--CH.sub.2 --O--[C.sub.n H.sub.2n O--].sub.m .fwdarw.Ch.sub.3 --CH.dbd.CH--O[C.sub.n H.sub.2n O--].sub.m
These propylene ethers do not participate in the hydrosilylation reaction and, because they cannot be separated economically from the polyethersiloxane obtained, for example, by distillation, they remain in considerable amounts in the hydrosilylation product. When the polyether siloxanes are used, the propenyl ethers can interfere and lead to detrimental effects. However, a method which can prevent this rearrangement or, at least, largely suppress it is not yet known.
The use of polysiloxanes with (meth)acrylate ester groups linked over SiC groups as radiation curable coating agents is known from the German Patent 38 10 140.
These compounds can be obtained by reacting polysiloxanes of the general average formula ##STR1## wherein R.sup.1 groups are the same or different and in each case represent low molecular weight alkyl groups with 1 to 4 carbon atoms or phenyl groups,
R.sup.2 groups partly can have the meaning of the R.sup.1 groups and PA0 R.sup.2 groups remaining, to the extent of 70 to 100%, are hydroxy-functional groups of the formula --CH.sub.2 (CR.sup.3.sub.2).sub.n --(OCH.sub.2 CHR.sup.4).sub.m --OH, --CH.dbd.CH--CR.sup.3.sub.2 --OH or ##STR2## wherein R.sup.3 groups are the same or different and in each case represent an H group or an alkyl group with 1 to 4 carbon atoms, PA0 with the proviso that at least 1.8 hydroxy-functional groups are contained in the average molecule, PA0 a has a value of 1 to 1000 and PA0 b has a value of 0 to 10, PA0 R.sup.2 groups partially have the meaning of the R.sup.1 groups and the PA0 R.sup.2 groups remaining to the extent of 70 to 100% are conventional epoxy-functional groups and to the extent of PA0 with the proviso that at least 1.8 epoxy groups are contained in the average molecule PA0 a has a value of 1 to 1,000 and PA0 b has a value of 0 to 10, PA0 R.sup.2 groups partially can have the meaning of the R1.sup.1 groups, PA0 R.sup.2 groups remaining to the extent of PA0 a has a value of 1 to 1,000 and PA0 b has a value of 0 to 10, PA0 70 to 100% of the R.sup.2 groups which do not have the meaning of the R.sup.1 group are R.sup.3 --R.sup.4 groups and PA0 0 to 30% of the R.sup.2 groups which do not have the meaning of the R.sup.1 group are alkyl groups with 2 to 12 carbon atoms or hydrogen groups. PA0 R.sup.9 groups partly can have the meaning of the R.sup.1 groups and PA0 R.sup.9 groups remaining to the extent of 70 to 100% are groups of the formula R.sup.3 --R.sup.10, in which
R.sup.4 groups are the same or different and in each case represent an H group of an alkyl group with 1 to 10 carbon atoms, and the subscripts PA1 n=0 to 10 and PA1 m=0 to 40, and to the extent of 30 to 0%, are optionally substituted alkyl groups with 2 to 20 carbon atoms and/or hydrogen groups, PA1 30 to 0% are alkyl groups with 2 to 10 carbon atoms or hydrogen groups, PA1 70 to 100% are groups of the formula R.sup.3 --R.sup.4, in which
with 0.4 to 0.9 molar amount of (meth)acrylic acid and up to 0.6 molar amount of a monocarboxylic acid which is free of double bonds capable of polymerizing based on the hydroxyl groups, with the proviso that the sum of the molar amount of acid does not exceed 1.0, under the usual esterification conditions.
Also with this method, there is risk that the double bond of the .alpha.-unsaturated, .omega.-OH component will isomerize in the course of the platinum-catalyzed addition reaction to the hydrogen siloxane. While thus formed propenyl alcohol which rearranges to the propionaldehyde can be distilled off from the addition reaction product, the propenyl polyether remains in the product. Since the propenyl polyether is not silicone-modified, it can adversely affect the abhesiveness of the product.
German patent 38 20 294 is an example of the state of the art for polysiloxanes which have ester groups at a spacer group linked by an SiC bond. This patent relates to polysiloxanes with (meth)acrylate ester groups linked through SiC groups. They can be obtained by reacting polysiloxanes of the general, average formula ##STR3## wherein R.sup.1 groups are the same or different and in each case represent low molecular weight alkyl groups with 1 to 4 carbon atoms or phenyl groups
with 0.4 to 0.9 molar amount of (meth)acrylic acid based on the epoxy groups, and reacting remaining epoxide groups with a monocarboxylic acid with 2 to 12 carbon atoms which is free of double bonds that are capable of polymerizing.